Underground mines utilize vertical shafts to provide access to underground workings. Conveyances (commonly called skips and cages) operate in the shaft and carry material and men. The conveyances run on guides which maintain proper orientation of the conveyance to the loading and unloading stations, keep the conveyances separated as they pass through the shaft and keep the conveyances from striking the shaft walls.
A typical guide system for the conveyances is referred to as a fixed or rigid guide system and utilizes wood timbers, rails, or structural tubing rigidly anchored to the shaft walls at intervals ranging from about 6 to 15 feet. More particularly, the guide timbers or rails are fixed to bunton sets (frames) fixed horizontally to the shaft wall. Mine shafts also supply ventilating air to the workings and the bunton sets resist air movement by causing turbulent airflow. This increases the power requirements for ventilating purposes.
Wire rope guide systems have been proposed to reduce the resistance to ventilating airflow and reduce the installation cost. The wire rope is a special type and is suspended from the headframe structure at the surface. The wire rope has great strength and rather small diameter which detracts from its utility since it provides a small surface for the guides on the conveyance.
Furthermore, if the conveyance is used for carrying men, it must be provided with a safety device to prevent free drop of the conveyance should the hoist cable break. The cable surface area is small and made up of many strands of wire. Therefore; actuation of the safety device (brake) can readily deform the rope and/or break strands and cause the rope to become unserviceable or fail totally. The wire rope simply can't take the extremely high crushing loads involved in setting the safety device.
In the past it has been proposed to use pipe for guide systems, but any such use has been limited to very short distances such as in buildings having only a few floors, etc. There are various reasons why pipe guide systems have not been used in deep shaft mines. The entire load of thousands of feet of pipe has to be carried by the threaded connections between the pipes. Ordinary pipe cannot stand this type of service. Past suspension systems resulted in stress concentrations at the headframe and this could cause failure of the suspension. It is difficult to inspect pipe guides. Ordinary pipe cannot safely be subjected to the crushing loads applied by a safety device in stopping the free fall of a 50 ton conveyance, for example.
With this as the background, the present invention proposes to use a suspended pipe guide system for deep mine shafts.
Using a pipe guide system which overcomes the objections to prior proposals will permit a lower cost installation and reduction in the cost of supplying ventilating air to the mine.